With a fretted and stringed electric or electronic musical instrument, musical sound is produced with various tones generated through detection of the timings at which strings are plucked and the locations of the fret members against which the strings being plucked are pressed on the fingerboard. The location of the fret member against which a string is pressed can be detected by the use of an electromagnetic pickup device responsive to the vibrations of the string for producing an analog signal varying with the waveform of the vibrations. The signal thus produced by the magnetic pickup device is monitored to detect the peaks of the signal waveform for determining the location of the fret member from the time interval between successive two peaks of the waveform. The detection of the locations of the fret members on the basis of such a signal however involves a problem in that the signal is produced with a considerable amount of delay after the player has plucked the string. This delay gives the player of the instrument a feeling of mistiming.
With a view to providing a solution to such a problem, an electronic musical instrument is proposed in Japanese Patent Application No. 60-240138 which relates to an electronic musical instrument having a fret-position sensor of a supersonic wave type. The fret-position sensor comprises piezoelectric transducer elements provided in conjunction with the individual strings of the musical instrument and responsive to timing signals cyclically supplied from a control circuit. Each of the piezoelectric transducer elements is operative to generate vibrations with a certain supersonic frequency each time the piezoelectric transducer element is activated with a timing signal. The vibrations generated by the piezoelectric transducer element are transmitted through the string engaged by the piezoelectric transducer element to the fret member against which the string is currently pressed. The vibrations which have reached the particular fret member are then "reflected" backwardly from the fret member to the piezoelectric transducer element and enable the sensor to produce an electric signal when the vibrations reflected are returned to the sensor. From the electric signal thus produced by the piezoelectric transducer element is detected the time duration for which the vibrations have been transmitted to the fret member and backwardly from the fret member to the piezoelectric transducer element. Such a time duration depends on the distance of the fret member from the piezoelectric transducer element and is accordingly representative of the location of the fret member with respect to the piezoelectric transducer element. Thus, the location of the fret member against which a string is pressed is in this manner detected from the electric signal supplied from the piezoelectric transducer element associated with the string.
In the meantime, there is known and used a "bent-string" playing technique with which a string is forced to sidewise slide on a fret member to produce a rising intonation. When such a technique is used during playing of a musical instrument having a fret-position sensor of the described nature, the sensor could not detect the mode of playing and for this reason the sound producing system could not produce the player's intended rising intonation. This is primarily because of the fact that the sensor depends for its operation merely on the period of time for which vibrations are transmitted to a fret member and backwardly from the fret member to the sensor.
The present invention contemplates elimination of such a drawback inherent in a prior-art fret-position sensor of the described nature and accordingly in an electric or electronic sound producing system using such a fret-position sensor in a musical instrument of the fretted and stringed type.